The present invention relates to a technology of printing slightly adherent plastic bases, especially polyoxymethylene or polypropylene products. The technology of the invention is applicable, e.g., to the printing of necessary information on shutters, made of polyoxymethylene or polypropylene, for opening and closing the head windows of floppy disks.
Plastic products, such as polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyoxymethylene (POM=polyacetal), polycarbonate (PC), and acrylonitrile-butadiene-styrene (ABS), are in use over a broad range of applications. Those plastic articles are printed, according to the uses, by a variety of techniques including screen printing, padding, and pad printing.
In the printing of the plastic products, the use of a thermosetting or thermoplastic ink can have adverse effects upon the objects, e.g., by the heat of curing or drying or by the action of the solvent used with the ink. The ink of the thermosetting type takes so much time for curing after the printing that its curing is a major limiting factor for the overall production process. To overcome these difficulties, printing with an ultraviolet-curing ink that completes curing immediately after application is being extensively accepted.
Nevertheless, the ultraviolet-curing ink is deemed practically out of use with the above-mentioned polyoxymethylene and polypropylene products. Those resins are in wide use (e.g., for the shutters to open and close the head windows of floppy disks) owing to their relatively low prices and good physical properties and moldability. However, they are too low in surface activity to produce adequate bond with inks, especially with the ultraviolet-curing ink, for practical use. Where they are to be printed, a thermosetting ink of two-part liquid type (consisting of a principal agent and a curing agent) is used. This combination is not suited for quantity production and makes printing barely possible. In cases when printing with an ultraviolet-curing ink is a necessity, those plastic bases have to be replaced by other materials.